The basin-fill sequence from the Tertiary Bicorp Basin (Eastern Spain) comprises a lower alluvial unit and an upper lacustrine unit. The lower part of the lacustrine unit includes a tuff bed, interbedded between two mammal-bearing horizons which have yielded fossil rodents characteristic of the MN 10 standard Mammal Unit (Late Vallesian, Late Miocene). K-Ar age determinations on the tuff have provided a radiometric age averaging 9.6 ± 0.2 Ma (weighted average of two samples) for this ash fall deposit. The stratigraphic correlation between the fossil mammal sites and the radiometrically-dated tuff allows a more precise calibration between the Late Miocene biochronologic and geochronometric scales. The Bicorp tie point constrains the calibration of the Late Vallesian to around 9.7 Ma, the ensemble of data suggesting ages of 10-11 Ma for the Early/Late Vallesian boundary and 9.5-8.5 Ma for the Vallesian/Turolian boundary.

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